awk -F, '{ country = $1;print country;}' metals.txt | sort | uniq | wc -l
grep -E '中国,|中国台北,|中国香港,' metals.txt | sort -t',' -k2,2nr -k3,3nr -k4,4nr
sort -t',' -k4nr metals.txt | head -n 5 | cut -d',' -f1
sort -t, -k2 -nr metals.txt | head -n 5 | tee >(awk -F, '{sum += $2} END {print "" sum}')
